Plasticizer-containing polyvinyl alcohol granules

ABSTRACT

For the thermoplastic processing of polyvinyl alcohol, the processing temperature must be below the decomposition temperature of the polyvinyl alcohol; this is attained by incorporating plasticizers. For preparing a plasticizer-containing granular polyvinyl alcohol wherein the plasticizer is homogeneously distributed, there is used as starting material a granular polyvinyl alcohol consisting substantially of particles having a definite diameter. The plasticizer is incorporated in the presence of a small amount of water insufficient to dissolve the polyvinyl alcohol, and the temperature is adjusted in a definite manner during the mixing operation. Simultaneous presence of fine particles of a high molecular weight organic compound soluble or dispersible in water is advantageous. The plasticizer-containing granular polyvinyl alcohol is suitable for the manufacture of any shaped articles, especially films and sheets.

This application is a continuation, of application Ser. No. 343,114,filed 1/27/82. which is a divisional application of Ser. No. 211,627filed Dec. 1, 1980, now U.S. Pat. No. 4,323,492 dated Apr. 6, 1982,which in turn is a continuation of application Ser. No. 022,869 filedMar. 21, 1979, now abandoned.

It is known that polyvinyl alcohol (PVAL) cannot be processedthermoplastically without difficulty because it decomposes below thesoftening temperature. For thermoplastic processing it is thereforenecessary to the softening temperature. This is generally achieved byincorporating plasticizers.

Commercial PVAL is generally available in powder form. Homogeneousincorporation of plasticizers into such a product is handicapped by thefact that the PVAL particles, depending on their size, absorb varyingamounts of plasticizer. Thermoplastic processing of plasticizercontaining PVAL therefore often results in shaped articles wherein theplasticizer is inhomogeneously distributed, which adversely affects theproperties of these articles.

The manufacture of plasticizer-containing polyvinyl alcohol has beenproposed in German Offenlegungsschrift No. 23 02 871 (British Pat. No.14 10 744). In this process, the intended homogenization of PVAL andplasticizer is attained by mixing the PVAL wetted and swollen by meansof methanol with the plasticizer and subsequently removing the methanol.However, there is no disclosure as to the grain size of the PVAL used.Moreover, the process has the disadvantage of requiring PVAL wetted bymethanol for incorporating the plasticizer. Therefore, commercial dryPVAL granules cannot be used.

It is the object of this invention to provide PVAL granules which arepourable and capable of being processed thermoplastically due to theircontent of plasticizer. A further object is to ensure that the PVALparticles have a substantially uniform and large size, and that theplasticizer contained in these particles is distributed as homogeneouslyas possible. These and other objects and advantages will be apparentfrom the specification and claims.

The present invention provides a plasticizer-containing, pourable,tack-free granular polyvinyl alcohol capable of being processedthermoplastically, wherein at least 70 weight % of the granular PVALconsist of particles having a diameter of from 0.8 to 4 mm andcontaining a plasticizer in homogeneous distribution.

The invention also provides a process for the manufacture of aplasticizer-containing, pourable, tack-free granular polyvinyl alcoholcapable of being processed thermoplastically by mixing polyvinyl alcoholgranules with a plasticizer, which comprises intensely and homogeneouslymixing 100 parts by weight of dry polyvinyl alcohol granules 70% ofwhich at least consist of particles having a diameter of from 0.4 to 4mm and from 5 to 50 parts by weight of a plasticizer, in the presence ofan amount of water insufficient for dissolving the PVAL under normalconditions, and raising and then decreasing the temperature of themixture during the mixing operation in such a manner that the polyvinylalcohol particles swell and temporarily agglomerate.

A preferred embodiment of the invention provides a process for themanufacture of a plasticizer-containing, pourable, tack-free granularpolyvinyl alcohol capable of being processed thermoplastically by mixingpolyvinyl alcohol granules with a plasticizer, which comprises intenselyand homogeneously mixing 100 parts by weight of dry polyvinyl alcoholgranules of which at least 70% consist of particles having a diameter offrom 0.4 to 4 mm and from 5 to 50 parts by weight of a plasticizer, inthe presence of an amount of water insufficient for dissolving the PVALunder normal conditions, and raising and then decreasing the temperatureof the mixture during the mixing operation in such a manner that thepolyvinyl alcohol particles swell and temporarily agglomerate, andwherein the components are mixed in the presence of from 1 to 15 partsby weight of a fine-particle high molecular weight organic compoundsoluble or dispersible in water and consisting of particles having adiameter not exceeding 300 micrometers (μm).

The invention additionally provides the granular polyvinyl alcoholobtained according to the above processes.

The PVAL used as starting material in accordance with the invention isprepared in known manner by saponification, preferably by alcoholysis,from polyvinyl esters, preferably polyvinyl acetate (see for exampleGerman Pat. No. 17 20 709 , which corresponds to British Pat. No. 11 68757). The 4 weight % aqueous solution of the PVAL has a viscosity offrom 4 to 70 mPa·s, preferably 10 to 60 mPa·s (measured at a temperatureof 20° C.). The ester number is in the range of from 10 to 250 mg KOH/g,preferably 20 to 200 mg KOH/g.

A characteristic feature of the invention is the use of PVAL granuleswhich consist substantially of particles having a definite size asstarting material for the manufacture of the intendedplasticizer-containing product. At least 70 weight %, preferably atleast 90 weight %, of the starting PVAL granules should consist ofparticles having a diameter of from 0.4 to 4 mm, preferably 0.6 to 3 mm.The remainder of a maximum 30 weight %, preferably a maximum 10 weight%, of starting material consists substantially of particles having asmaller diameter, which is not disadvantageous because these fineparticles, on mixing with the plasticizer, agglomerate nearly completelyto form coarse particles. The PVAL granules obtained as final productare tack-free, easily pourable and can be processed thermoplastically.The substantial part thereof, that is at least 70 weight %, preferablyat least 90 weight %, consists of particles having a diameter of from0.8 to 4 mm, preferably 1 to 3.5 mm.

A further characteristic of the invention is the incorporation of theplasticizer into the dry granular PVAL in the presence of water in suchan amount which under normal conditions is insufficient for dissolvingthe PVAL used. Depending on the kind of PVAL, this amount of water isfrom 2 to 40 weight %, preferably 4 to 30 weight % (relative to thepolyvinyl alcohol). Removal of the water still present after completionof the mixing operation is not required.

Suitable plasticizers are above all aliphatic polyols having a boilingpoint above 250° C., especially bihydric to hexahydric alkanols havingfrom 2 to 6 carbon atoms; bi- or trihydric alkanols are preferably used.Examples are ethyleneglycol, glycerol, trimethylolpropane,neopentylglycol and sorbitol. Instead of a single plasticizer, a mixtureof different plasticizers may be used. The amount of plasticizer to beincorporated is in the range of from 5 to 50 weight %, preferably 10 to30 weight % (relative to the polyvinyl alcohol).

Temperature control during the mixing operation is very important forthe process of the invention. The temperature of the mixture must beadjusted in such a manner that the starting PVAL particles swell andagglomerate temporarily. To achieve this, the temperature of the mixturefirst has to be gradually raised from the starting room temperature to amaximum and then decreased again, thus causing the formation of loosePVAL agglomerates during the temperature rise which easily decomposeafter the maximum has been passed. The maximum temperature does notexceed 140° C. and is preferably in the range of from 100° to 130° C.:in the cooling phase the temperature is reduced to 40° to 70° C.,preferably 35° to 60° C. The temperature is raised and decreasedpreferably in about similar periods of time.

A special embodiment of the invention is characterized by mixing thegranular polyvinyl alcohol and the plasticizer in the presence of from 1to 15 parts by weight, preferably 2 to 12 parts by weight (relative to100 parts of granular polyvinyl alcohol) of a fine-particle highmolecular weight organic compound soluble or dispersible in water, theparticle diameter of which is generally a maximum 300 μm, preferablyfrom 0.1 to 300 μm. The average polymerization degree (average weight_(P).sbsb.w) of this high molecular weight compound is at least 200, andpreferably from 300 to 5000.

The high molecular weight compound may be natural or synthetic. Suitableare, for example, starch and starch derivatives, cellulose derivativessuch as methyl cellulose and carboxyhydroxy cellulose, casein andgelatin, and especially vinyl polymers. Suitable vinyl polymers are forexample polyvinyl alcohol itself and derivatives thereof, especiallypolyvinyl esters such as polyvinyl acetate and polyvinyl propionate,polyvinyl acetals such as polyvinylformal or polyvinylbutyral.Copolymers of different vinyl compounds may likewise be used, preferablycopolymers of vinyl acetate with ethylene, maleic acid diesters, fumaricacid diesters, acrylic acid esters, methacrylic acid esters oracrylonitrile, the alcohol component of the cited esters havingpreferably from 2 to 8 carbon atoms.

The high molecular weight compound is generally used in the form of apowder which is obtained pereferably by spray-drying of a correspondingsolution or dispersion. The diameter of the powder particles isadvantageously from 10 to 300 micrometers, preferably 20 to 200micrometers. According to an especially preferred embodiment of theprocess of the invention the high molecular weight compound is used inthe form of an aqueous dispersion. In this case, the particle diameterof the disperse compound is advantageously in the range of from 0.1 to10 micrometers, preferably in the range of from 0.2 to 8 micrometers.

Preferably, the high molecular weight compound is added to the PVALgranules before adding the plasticizer; alternatively, it may be addedto the granular PVAL simultaneously or in admixture with theplasticizer.

Depending on the kind and the amount of the components and the kind ofmixing equipment, a period of from 10 minutes to 3 hours is required forthe entire mixing operation. While mixing the dry PVAL particles withthe liquid plasticizer/water mixture the particles swell, whichfacilitates diffusion of the plasticizer into the interior of theparticles.

The plasticizer must be distributed as homogeneously as possible in thePVAL particles. This is attained by using such mixing equipment whichensures intense and permanent intermixing of the components. Especiallysuitable are forced circulation mixers having vertically or horizontallyarranged agitators, and planetary mixers. Advantageously, the mixers areprovided with heating and cooling devices. The above temperature rise isensured by friction or jacket heating, depending on the kind of mixingequipment.

The process of the invention may likewise be carried out continuously,for example, in horizontally positioned reaction tubes with a paddleagitator or screw, or in continuously operating kneaders, each beingprovided with the necessary heating and cooling zones.

Auxiliaries facilitating the processing of the granular PVAL may also beincorporated into the granules, especially lubricants, such as stearicacid, waxes, polyethyleneglycols having a molecular weight of from 400to 20,000, fine-particle silicic acid and alkaline earth stearates,preferably calcium stearate, furthermore heat stabilizers and dyestuffs.The total amount of such auxiliaries is 3 weight % at most, preferablyfrom 0.04 to 1.0 weight % (relative to the polyvinyl alcohol).

The granular PVAL of the invention can be molded thermoplasticallywithout any difficulty, for example, by compression molding, injectionmolding and extrusion, and it is suitable for the manufacture of anyshaped articles, for example, plates, tubes, profiles, fibers and,especially, films and sheets.

The easy processability of the granular PVAL of the invention is aboveall due to the fact that by mixing starting material and plasticizer inthe presence of a fine-particle high molecular weight organic compound,the PVAL particles become uniform, which considerably facilitatesplastication during the processing. Moreover, some of the high molecularweight compounds have a pronounced lubricating effect.

The following examples and the corresponding diagrams illustrate theinvention.

FIG. 1 indicates the temperature curve of the process according toexamples 1 to 3.

FIGS. 2 to 5 demonstrate the effect of the process of the invention,that is, increase and uniformization of the size of the PVAL granules;they indicate the grain size distribution of the corresponding startingmaterials (curve 1) and the final product (curve 2) determined by sieveanalysis. There are plotted on the abscissa the particle diameter (mm)and on the ordinate the sieve passage (%); the inclination of the curvesbeing a measure for the uniformity of the PVAL particles.

EXAMPLE 1

6 kg of a commercial granular PVAL, the particles of which have adiameter in the range of from 0.6 to 3 mm, which has an ester number of140 mg KOH/g and the 4 % aqueous solution of which has a viscosity of 18mPa·s, are introduced into a 35 liter forced circulation mixer. Withagitation and at room temperature, a mixture of 750 g of glycerol and240 g of water is added within 1 minute, the agitation speed being 1,200rpm. After about 4 minutes the PVAL particles begin to agglomerate, andafter about 17 minutes the agglomerates are broken up or crushed again.During the mixing operation, the temperature rises to 105° C. within 15minutes, and it is reduced within 10 minutes to 50° C. by slowing downthe agitation speed to 600 rpm and by jacket cooling (temperature curve:see FIG. 1, curve a). Subsequently, the plasticizer-containing granularPVAL is let off. It consists of particles having a diameter in the rangeof from 1 to 4 mm, it is well pourable, and it can be processed on asingle-screw extruder to give a completely perfect blown film having athickness of 30 μm.

Repetition of this Example in a 160 liter forced circulation mixer givesidentical results.

EXAMPLE 2

Example 1 is repeated with the following exceptions: The starting PVALparticles have a diameter in the range of from 0.6 to 2.5 mm, the PVALhas an ester number of 90 mg KOH/g and the viscosity of its 4% aqueoussolution is 30 mPa·s. The amount of glycerol is 1,050 g and that ofwater 300 g. After about 3 minutes the PVAL particles begin toagglomerate, and after about 16 minutes the agglomerates are broken upor crushed again. The temperature rises during the mixing operation to105° C. (temperature curve see FIG. 1, curve b). Theplasticizer-containing PVAL granules have a diameter in the range offrom 0.9 to 3.5 mm, and they can be processed according to Example 1 togive a completely perfect blown film.

EXAMPLE 3

Example 1 is repeated with the following exceptions: The PVAL particleshave a diameter in the range of from 0.5 to 2.5 mm, the PVAL has anester number of 20 mg KOH/g and the viscosity of the 4 % aqueoussolution is 20 mPa·s. The amount of glycerol is 1,500 g and that ofwater 900 g. In addition, 3 g of calcium stearate are introduced intothe mixer. After about 6 minutes, the PVAL particles start toagglomerate, and after about 16 minutes the agglomerates are crushedagain. During the mixing operation, the temperature rises to 80° C. andis raised further to 110° C. by additional heating (temperature curvesee FIG. 1, curve c). The plasticizer-containing granular PVAL consistsof particles having a diameter in the range of from 0.9 to 3.3 mm, andit can be processed according to Example 1 to give a completely perfectblown film.

EXAMPLE 4

1 kg of the PVAL granules used in Example 1 are introduced into a 5liter mixer having a planetary agitator, and mixed under the conditionsof Example 1 with a solution of 100 g of trimethylolpropane and 2 g ofpolyethyleneglycol (molecular weight 1,500) in 30 g of water. Heating isensured in this case be jacket heating. The temperature curve isidentical to that of Example 1, and the plasticizer-containing granularPVAL corresponds to that obtained according to Example 1.

EXAMPLE 5

A mixture of 6.0 kg of a commercial granular PVAL (ester number: 90 mgKOH/g, viscosity of the 4 weight % aqueous solution 30 mPa·s, particlediameter 0.5 to 3 mm) and 0.3 kg of a polyvinyl acetate powder (averagepolymerization degree 1,500, particle diameter 20 to 200 μm) isintroduced into the mixer used in Example 1. With agitation (1,200 rpm)and at room temperature, a mixture of 1.2 kg of glycerol and 0.3 kg ofwater is added to the above mixture. After about 3 minutes the PVALparticles start to agglomerate, and after about 16 minutes theagglomerates are crushed again. During the mixing operation, thetemperature rises to 105° C. within 15 minutes, and it is reduced within10 minutes to 50° C. by jacket cooling and reduction of the agitationspeed to 600 rpm. Subsequently, the plasticizer-containing granular PVALis let off which consists of particles having a diameter in the range offrom 1.2 to 3.7 mm. It is well pourable and tack-free. The grain sizedistribution of the starting material (curve 1) and the final product(curve 2) is shown in FIG. 2.

EXAMPLE 6

6.0 kg of a commercial granular PVAL (ester number 20 mg KOH/g,viscosity of the 4 weight % aqueous solution 20 m.Pa·s, particlediameter 0.6 to 2.5 mm) are introduced into the mixer used in Example 1.With agitation (1,200 rpm) and at room temperature, a mixture of 1.05 kgof glycerol, 0.3 kg of water and 1.2 kg of a 50 weight % aqueouspolyvinyl acetate dispersion (average polymerization degree 1,500,particle diameter 0.6 to 6.0 μm) is added. After about 3 minutes thePVAL particles start to agglomerate, and after about 16 minutes theagglomerates are crushed again. During the mixing operation, thetemperature is raised with 10 minutes to 110° C. and then reduced within15 minutes to 50° C. by jacket cooling and reduction of the agitationspeed to 600 rpm. Subsequently, the plasticizer-containing granular PVALis let off which consists of particles having a diameter in the range offrom 0.45 to 4.0 mm. It is easily pourable and tack-free. The grain sizedistribution of the starting material (curve 1) and the final product(curve 2) is shown in FIG. 3.

EXAMPLE 7

A mixture of 6.0 kg of a commercial granular PVAL (ester number 140 mgKOH/g, viscosity of the 4 weight % aqueous solution 18 mPa·s, particlediameter 0.4 to 4.0 mm) and 0.15 kg of a polyvinyl butyral powder(average polymerization degree 1,600, particle diameter 100 to 200 μm)is introduced into the mixer used in Example 1. With agitation (1,200rpm) and at room temperature, a mixture of 0.75 kg of glycerol and 0.24kg of water is added. After about 3 minutes the PVAL Particles start toagglomerate, and after about 16 minutes the agglomerates are crushedagain. During the mixing operation, the temperature rises to 105° C.within 15 minutes and it is reduced to 50° C. within 10 minutes by meansof jacket cooling and reduction of the agitation speed to 600 rpm.Subsequently, the plasticizer-containing PVAL granules are let off whichhave a diameter in the range of from 0.9 to 4.0 mm, are well pourableand tack-free. The grain-size distribution of the starting material(curve 1) and the final product (curve 2) is shown in FIG. 4.

EXAMPLE 8

6.0 kg of a commercial granular PVAL (ester number 140 mg KOH/g,viscosity of the 4 weight % aqueous solution 18 mPa·s, particle diameter0.4 to 4.0 mm) are introduced into the mixer used in Example 1. Withagitation (1,200 rpm) and at room temperature, a mixture of 0.75 kg ofglycerol, 0.3 kg of water and 0.12 kg of a 50 weight % aqueous vinylacetate/dibutyl maleate copolymer dispersion (monomer ratio 50:50,average polymerization degree 1,200, particle diameter 0.6 to 6.0 μm) isadded. After about 3 minutes the PVAL particle start to agglomerate, andafter about 16 minutes the agglomerates are crushed again. During themixing operation the temperature rises within 13 minutes to 110° C. andis then reduced to 50° C. within 12 minutes by jacket cooling andreduction of the agitation speed to 600 rpm. The plasticizer-containingPVAL granules are then let off which have a diameter in the range offrom 1.0 to 4.0 mm, are easily pourable and tack-free. The grain sizedistribution of the starting material (curve 1) and the final product(curve 2) is shown in FIG. 5.

What is claimed is:
 1. A plasticizer-containing, pourable and tack-freegranular polyvinyl alcohol composition comprising polyvinyl alcohol, atleast 90% of the plasticized polyvinyl alcohol granules being from 0.8to 4 mm in diameter; a plasticizer homogeneously distributed therein,the plasticizer being present in an amount of 10 to 30% by weightrelative to the unplasticized polyvinyl alcohol granules; and furthercontaining, distributed homogeneously therein, a fine particle highmolecular weight organic compound, in an amount of 2 to 12% by weightrelative to the unplasticized polyvinyl alcohol granules, which issoluble or dispersible in water.
 2. The composition of claim 1, whereinthe high molecular weight organic compound is a starch, starchderivative, cellulose, cellulose derivative, casein, gelatin or vinylpolymer.
 3. The composition of claim 2, wherein the cellulose derivativeis methyl cellulose or carboxyhydroxy cellulose.
 4. The composition ofclaim 2, wherein the vinyl polymer is polyvinyl ester or polyvinylacetal.
 5. The composition of claim 2, wherein the vinyl polymer is acopolymer of vinyl acetate with ethylene, maleic acid diesters, fumaricdiesters, acrylic acid diesters, methacrylic acid esters oracrylonitrile, the alcohol portion of the esters having 2 to 8 carbonatoms.
 6. The composition of claim 1, wherein the high molecular weightcompound is in the form of powder particles having diameters of from 10to 300 micrometers.
 7. The composition of claim 6 wherein the diametersof the high molecular weight compound particles are from 20 to 200micrometers.
 8. The composition of claim 1, wherein the high molecularweight compound is in the form of an aqueous dispersion in which theparticle diameter of the disperse compound is from 0.1 to 10micrometers.
 9. The composition of claim 8, wherein the particlediameter is from 0.2 to 8 mircometers.
 10. The composition of claim 1,further including up to 3% by weight of an auxiliary comprising a heatstabilizer, a dyestuff and a lubricant selected from the groupconsisting of stearic acid, wax, polyethylene glycol having a molecularweight of from 400 to 20,000, silicic acid and an alkaline earthstearate, or a combination thereof.
 11. The composition of claim 10,wherein the auxiliary or auxiliaries are present in amounts of from 0.4to 1.0% by weight relative to the polyvinyl alcohol granules.
 12. Thecomposition of claim 1, wherein the plasticizer is an aliphatic polyolhaving a boiling point above 250° C.
 13. The composition of claim 12,wherein the plasticizer is ethyleneglycol, glycerol, trimethylolpropane,neopentylglycol or sorbitol.
 14. The composition of claim 1, wherein theplasticizer is glycerol and further including a high molecular weightcompound which comprises a polyvinylacetate which is dispersible inwater.
 15. The composition of claim 1, wherein at least 70 weight % ofthe polyvinyl alcohol granules consist of particles having a diameter of1 to 3.5 mm.
 16. The composition of claim 15, wherein at least 90% ofthe polyvinyl alcohol granules consist of particles having a diameter of1 to 3.5 mm.
 17. The composition of claim 1, wherein the fine particlehigh molecular weight organic compound has a particle diameter size offrom 0.1 to 300 μm and a polymerization degree (average weight) of from300 to 5000; and the composition further contains auxiliaries, in anamount from 0.04 to 1% by weight, including a heat stabilizer, adyestuff and a lubricant selected from the group consisting of stearicacid, wax, polyethyleneglycol having a molecular weight of from 400 to20,000, silicic acid and an alkaline earth stearate.